American Therapist wanting to open private practice in UK

Hi I am American therapist. My friend and I would love to open a private practice in the UK or Netherlands. I don't know how that would work and where to start in researching how to accomplish that. I have emailed three American therapist that I saw online have a private practice in London and Amsterdam hoping they reply back to me. However, does anyone have any information on how I can open my own private practice as American overseas? All information will be greatly appreciated.